The use of soluble fluoride salts, such as stannous fluoride and sodium fluoride, to reduce the incidence of dental caries in the general population is a well known and ongoing endeavor. The administration of these fluoride compounds takes many forms, including the fluoridation of drinking water, professional treatment by dentists and incorporation in oral hygiene compositions such as dentifrices and mouthrinses.
It is also known that zinc plays a role in dental care. For example, in U.S. Pat. No. 4,160,821 issued July 10, 1979, there is disclosed a composition for treating gingivitis comprising a vehicle containing a high concentration of glycerol and a zinc salt, such as zinc chloride, that is soluble in the glycerol. In an article entitled "A Study of Zinc In Human Teeth," Arch. Oral Biol., Vol. 8, pp 135-144. 1963. Pergamon Press Ltd. (Printed in Gt. Britain), the authors, citing reports of animal studies in earlier publications by McClure (1948, Observations on induced caries in rats. J. dent. Res. 27, 34-40) and Mansell and Hendershot (1960, The spectrochemical analysis of metals in rat molar enamel, femur and incisors. Arch. oral Biol. 2, 31-37) note the relatively high level of zinc in teeth, and indicate that while the significance of the presence of zinc in teeth is uncertain and there is no evidence that zinc reduces caries in man or experimental animals, the relationship between zinc concentration in enamel and caries susceptibility should be elucidated before this element can be dismissed as a factor in dental health. An abstract of a paper entitled "Fluoride Content in Enamel After Topical Applications of AlCl.sub.3, ZnCl.sub.2 and NaF" presented at the 25th ORCA Congress, Caries Res. 13(2):99,1979 reports on in vitro experiments conducted on 3 groups of 10 permanent teeth each and concludes that pretreatment with AlCl.sub.3 results in an appreciable increase of F.sup.- in the enamel surface but that the increase was distinctly lower in teeth treated only with NaF or pretreated with ZnCl.sub.2.
In British Patent Specification No. 1,373,003, published Nov. 6, 1974, there is disclosed a dentifrice composition having activity against plaque and calculus on a tooth surface comprising a sparingly soluble zinc salt--which is defined as a zinc salt of an acid, other than zinc fluoride or its hydrates, having a water solubility greater than that of zinc phosphate and less than 1 gram of zinc per 100 ml of water at 20.degree. C.--and a mixture of detergents. The dentifrice may also contain a compatible abrasive such as alumina and other conventional toothpaste ingredients.
U.S. Pat. No. 4,146,606, issued Mar. 27, 1979, relates to a pharmaceutical composition for dental use that can, inter alia, suppress dental caries, this composition comprising a strontium compound, a zinc compound, tannin and, optionally, a fluorine compound in such a weight proportion that the weight ratio of strontium, zinc, tannin and fluorine is 1 to 3:2 to 4:1 to 3:0 to 4.
U.S. Pat. No. 4,138,477, issued Feb. 6, 1979, discloses a composition to prevent and control mouth odor, which is also said to be effective in preventing calculus, plaque, caries and periodontal disease, containing as the essential agent a zinc-polymer complex formed by the reaction or chelation of a zinc compound with an anionic polymer containing carboxylic, sulfonic and/or phosphoric acid radicals. The composition may also include, inter alia, a fluorine-containing compound that protects the teeth against decay.